Karl Deisseroth thinks with his hands as much as his mind. When I photographed him, his fingers rose instinctively to his temples, not as affectation but as posture, the way some people lean forward when listening closely. He is a psychiatrist, a neuroscientist, an engineer, a clinician, and a writer, but those labels only begin to describe what he has been doing for the past two decades. His real subject has always been the same difficult question. How does the brain generate experience, and how might we intervene when that experience becomes unbearable.
Deisseroth grew up drawn to both science and literature. Long before optogenetics made him a household name in neuroscience, he was reading poetry, thinking about consciousness, and wondering how biology gives rise to inner life. That dual impulse never left him. It shaped his path through Harvard, Stanford, and a career that refused to choose between the clinic and the lab. He treats patients who are living inside depression, addiction, and psychosis, and then walks back into the lab to ask what is happening, cell by cell, circuit by circuit, when a mind begins to fracture.
In the mid 2000s, working with students and collaborators, Deisseroth helped create optogenetics, a technique that uses light to control the activity of specific neurons in living brains. It was an audacious idea that bordered on science fiction at the time. By inserting light sensitive proteins into targeted cells, researchers could turn neural circuits on and off with millisecond precision. For the first time, causality in the brain could be tested directly rather than inferred. The technique spread rapidly across neuroscience, reshaping how researchers study behavior, emotion, memory, and disease. It is now foundational, taught to students who were children when the first papers appeared.
Yet optogenetics was never the end point. It was a tool, a means to understand something larger. Deisseroth continued to push outward, developing new methods like CLARITY, which renders brain tissue transparent while preserving its molecular structure. Whole brains could now be visualized intact, their wiring traced in three dimensions. These advances were not about spectacle. They were about context. Mental illness, he understood, does not live in isolated cells but in networks that span regions and scales.
At Stanford, Deisseroth built a lab that feels more like an ecosystem than a hierarchy. Engineers, physicists, clinicians, and biologists work side by side. The conversations move easily from protein folding to patient care. His wife, neurologist and neuroscientist Michelle Monje, works just down the hall, studying how neural activity influences cancer growth in the brain. Their intellectual lives overlap in quiet, generative ways, visible in notebooks and shared questions rather than grand statements.
Alongside the science, Deisseroth writes. His book Projections is not a memoir in the conventional sense. It is a careful, compassionate exploration of what it means to live inside different minds, including his own. He writes about patients with the same precision he brings to experiments, never reducing them to diagnoses, never pretending that understanding eliminates mystery. The writing reveals something essential about him. He does not believe that explanation diminishes wonder. He believes it deepens responsibility.
Photographing Deisseroth, what struck me most was his stillness. This is someone whose work has accelerated entire fields, yet he moves deliberately, listens closely, and seems comfortable sitting with questions that do not resolve quickly. His impact is not only measured in citations or prizes, though there are many. It is measured in how a generation of scientists now thinks about the brain as something that can be understood without being simplified, and treated without being stripped of its humanity.
Karl Deisseroth is building maps of the mind. Not to conquer it, but to care for it.
